1. Technical Field
The present invention relates to a process for producing spherical silica particles, particularly a process for producing solid spherical silica particles having no depression or crack on the surface.
2. Background Art
Spherical silica particles are widely used for a catalyst, a catalyst support, a pigment for cosmetics, a column packing for chromatography, a resin filler, an adsorbent or a drying agent, from the viewpoint of varieties in the particle size, the pore structure and the surface physical properties. For such applications, in view of e.g. particle strength or packing density, solid spherical silica particles having no depression or crack on the surface are preferred.
As a process for producing the spherical silica particles, a method has been known wherein an aqueous sodium silicate solution or an alkyl silicate is emulsified in a solvent having no miscibility therewith, followed by gelation with e.g. an acid, an alkali or water (JP-A-4-154605). Further, a method has been known wherein an aqueous sodium silicate solution or an alkyl silicate is gelated with e.g. an acid, an alkali or water, followed by emulsification in a solvent having no miscibility therewith, for granulation (JP-B-4-2525). By such so-called emulsification methods, solid spherical silica particles having no depression can relatively easily be obtained.
Further, as a method for making the shape spherical, a spray method has been widely known. JP-A-61-168520 discloses a method of spray-drying a silica sol. JP-A-4-68247 discloses a method of spray-drying an alkali silicate. By such methods, spherical silica particles having a pore volume of at most about 0.5 cm.sup.3 /g can be obtained.
Further, JP-B-6-99135 discloses a method of carrying out wet grinding of a hydrogel, followed by spray drying. By the spray-drying method, hollow particles, depressions and cracks are likely to result, and to overcome these, JP-B-2-61407 proposes a two-stage drying method at a low drying rate and successively at a high drying rate. JP-B-2-61406 and JP-B-5-3412 disclose a spray-drying method by the wet air.